Various transport machines exist in the prior art for lifting, loading and stacking containers ranging from cranes and derricks to forms of straddle lift van carriers and lift trucks equipped with special gooseneck and lift frame attachment.
The containers themselves come in twenty or forty foot lengths and are standardized, in dimension for volumetric uniformity, as set forth in the American National Standards Institute (ANSI), 1430 Broadway Street, New York standards entitled "Specifications for Cargo Containers" (publication number MH5.1-1965).
It is common practice around docks, wharfs or transport terminals to use large lift trucks as container handlers by outfitting them with a gooseneck from which is suspended a lift frame, a rectangular structure having hydraulically extendable ends to accommodate either the twenty or forty foot container. At the corners of the lift frame are twist locks which engage standardized receptacles in upper corners of the container when the lift frame is lowered onto the container.
Such a lift frame is described in U.S. Pat. No. 3,764,032 issued Oct. 9, 1973 and titled "Container Handling Device" assigned to the assignee of the present invention.
The twist locks are constructed according to International Standards Organization requirements and are located at each corner of the frame. They are actuated from the operator's cab where green and red lights on the control console indicate the status of lock engagement with the container.
The lift frame is also capable of being hydraulically side shifted and turned or slewed relative to the lift truck by means of hydraulic cylinders actuated by the hydraulic circuit of the lift truck, however, in order to achieve the productivity gains sought that the maneuvering of the lift frame will allow, it is necessary for the operator to have adequate visibility of the twist locks and without also moving the lift truck, for rapid engagement with the corner fittings of the container in securing it to the lift frame.
The lift truck will have a hydraulically elevatable mast or upright often used with other attachments, such as forks, and for such purpose it is necessary to locate the operator's cab forward, close to the upright, for adequate visibility of the forktips in picking up loose loads or pallets. The optimum cab position for fork visibility is not the same as for maneuvering the lift frame when handling containers.
The lift truck will also have a structure, integral with the frame, overhanging the cab to protect the operator from falling loads, an overhead guard, the structural strength of which will meet or exceed the safety requirements of ANSI B56.1 and the Occupational Safety and Health Act, Subpart N Section 1910.178 for Powered Industrial Trucks. The overhanging portion will usually be a grill of ribs leaving openings for visibility at lift heights necessary for stacking shipping containers, nevertheless it has a tendency to reduce visibility from within the cab which has a window in the roof directly above the operator's station for the purpose of being able to see at such heights. The visibility is further restricted by the fact that the window is hard to keep clean beneath the overhead guard.
The lift truck frame will have massive side rails supporting a counterweight and steer axle at the rear, an engine, a drive axle housing at the front bolted to the frame having tandem gear reduction hubs, differential gearing and other drive line components placed within the housing and the upright or mast of the fork lift truck mounted on trunions at either end of the housing. Hydraulic cylinders are actuated from controls in the cab to back or forward tilt the upright on its trunion mountings to the axle housing.
It is also common for the upright of a heavy forklift truck, such as required for lifting containers having capacities which range up to eighty or even a hundred thousand pounds, to have a relatively massive upright structure. The upright will have parallel outer rails secured on trunions to the axle and a moveable inner rail section that telescopes within the outer rails when raised and lowered on rollers by a hydraulic cylinder. Chains anchored to a cross-member between the outer rails travel over sheaves at the top of the inner rail section and extend down the other side fastening on to a carriage which travels on rollers mounted on the inner rail section. The forks or other attachment are mounted on the carriage. When the truck is used for lifting containers, the forks are taken off and a gooseneck is attached to the carriage from which the lift frame is suspended on chains for converting the lift truck into a container handler.
The upright inner rail section is typically the same length as the outer rails to achieve maximum overlap of the roller sets in lifting the heavy loads. This creates a thicker rail cross-section when the upright is collapsed around which the operator must see in spotting containers on the tarmac.
It is common to exhaust the engine through a stack pipe directly behind the operator's cab which has a tendency to allow exhaust gases to be ejected over the top of the cab and to the rear which not only raises emission levels in the cab area, but also is a source of noise in the cab.
The hydraulic system of the lift truck will ordinarily have a pump for the upright lift and tilt cylinders driven off a torque converter from the engine, however lifting speeds adequate for heights usually found suitable for lift truck loads do not achieve the speeds desirable in container handling applications where thirty and forty-foot lifts are common.